A quantity which remains unchanged under certain classes of transformations. Invariants are extremely useful for classifying mathematical objects because they usually reflect intrinsic properties of the object of study.

**References**

Hunt, B. ``Invariants.'' Appendix B.1 in *The Geometry of Some Special Arithmetic Quotients.*
New York: Springer-Verlag, pp. 282-290, 1996.

© 1996-9

1999-05-26